1. Technical Field
The present invention relates to motors mounted in a variety of types of devices such as vehicles including cars and trucks, industrial devices, and electrical home appliances, and in particular, to full-pitch winding switched reluctance motors.
2. Related Art
Various types of switched reluctance motors are known as shown by Japanese Patent Laid-open Publication No. 8-126273 and Japanese patent No. 3157162.
FIG. 85 pictorially shows a section of a switched reluctance motor according to an example shown in such disclosures. The motor shown in FIG. 85 includes a stator 86K having six stator poles which are teeth 861, 862, 863, 864, 865 and 866 and a rotor having four salient poles. These elements are made of soft magnetic materials.
The U-phase stator pole 861 is wound by a U-phase winding which is a concentrated winding US1, which is shown by references 867 and 868 and a dashed line 86N. A reference 864 also shows a U-phase stator pole, which is wound by a concentrated winding US2 shown by references 86D and 86E and a dashed line 86P. Both windings US1 and US2 are electrically connected in series to each other, and, when being supplied with current, generate a magnetic flux φu shown by a reference 86M. This excitation will cause an attraction force at rotor salient poles 86L and 86Q, thus generating torque in the counterclockwise direction (CCW) illustrated by an arrow.
A reference 863 shows a V-phase stator pole, which is wound by a concentrated winding VS1 shown by V-phase windings 86B and 86C and a dashed line. A reference 866 also shows a V-phase stator pole, which is wound by a concentrated winding VS2 shown by V-phase windings 86H and 86J and a dashed line. Both windings VS1 and VS2 are electrically connected in series to each other, and, when being supplied with current, generate a magnetic flux φv at rotor salient poles located nearby, thus generating torque responsively to attraction forces thereat.
A reference 865 shows a W-phase stator pole, which is wound by a concentrated winding WS1 shown by W-phase windings 86F and 86G and a dashed line. A reference 862 also shows a W-phase stator pole, which is wound by a concentrated winding WS2 shown by V-phase windings 869 and 86A and a dashed line. Both windings WS1 and WS2 are electrically connected in series to each other, and, when being supplied with current, generates a magnetic flux φw at rotor salient poles located nearby, thus generating torque responsively to attraction forces thereat.
In the switched reluctance motor shown in FIG. 85, the torque for rotation can be generated continuously by sequentially exciting the U-, V- and W-phases in order to rotate the rotor. This motor has various features. Practically the motor is lower in production cost due to using no permanent magnets, and is simpler in structure because the stator windings are the concentrated windings. In addition, magnetic fluxes acting between the stator salient poles and the rotor salient poles act at saturation flux densities of magnetic steel sheets, so that the torque can be obtained on electromagnetic actions at higher magnetic flux densities. Furthermore, the rotor is robust, and the rotor can be rotated at higher speeds.
However, the switched reluctance motor shown in FIG. 85 has drawbacks. As the rotor rotates, positions at each of which a radial force acts between the stator and the rotor change 90 degrees in the circumferential direction. In addition, drive currents are given in a switched manner. For these reasons, in particular, the deformation of the stator in the radial direction thereof is relatively larger, causing vibration and noise to be larger. The use efficiency of the windings has also a drawback. Currents to generate the torque are supplied to four windings among the 12 windings shown in FIG. 85, so that the use efficiency of the windings is 4/12=⅓, which is lower. As a result of this, loss due to Joule heat, which is emitted from the windings, becomes larger.
A lateral section of another conventional motor is shown in FIG. 86. This is a switched reluctance motor with phase windings wound in a full pitch. References M11 and M14 show an A-phase winding wound in a full pitch. References M13 and M16 show a B-phase winding wound in a full pitch, and references M15 and M12 show a C-phase winding wound in a full pitch.
When a magnetic flux shown by a reference 86M is generated to pass through stator poles 861 and 864, currents are supplied to the two pairs of windings consisting of the A-phase windings M11 and M14 and the C-phase windings M15 and M12. For generating a magnetic flux passing through sartor poles 863 and 866, currents are supplied to the two pairs of windings consisting of the B-phase windings M13 and M16 and the A-phase windings M11 and M14. Similarly, for generating a magnetic flux passing through stator poles 865 and 862, currents are supplied to the two pairs of windings consisting of the C-phase windings M15 and M12 and the A-phase windings M11 and M14.
In comparison with the motor shown in FIG. 85, the switched reluctance motor shown in FIG. 86 has a feature that the winding resistance in each slot becomes smaller, approximately ½, because each of the windings is used to magnetically excite the stator poles located adjacent to each winding in the circumferential direction. Further, in the lower speed rotation, as explained above, rotor poles are sequentially excited by stator poles in order to generate the torque for the rotation. However, when the rotation is shifted from lower speeds to higher speeds, the magnetic flux interlinks with plural windings as stated, providing the magnetic flux with complex behaviors thereof. In consideration of this fact, supplying the currents to the windings in an exact manner becomes difficult, thus making it possible to correctly generate the torque in speed ranges other than a lower speed range.
Moreover, in the switched reluctance motor shown in FIG. 86, the full-pitch windings have long coil end portions. This results in a drawback that the rotor of the motor has a longer axial length. There is also a drawback that the resistance of the windings is larger, because the length of winding portions located outside the slots becomes longer. Further, the drawbacks of the switched reluctance motor shown in FIG. 85, which have been explained, are also true of the switched reluctance motor shown in FIG. 86.